How to link different parts of data blocks?
Create a Text and type ABC in edit mode, then create another text, go to the properties window, text panel: the first tab will show a dropdown menu with two datablock, named "text" and "text.001". 

Just assign the first ("text", wich is "ABC") to the second object and every time you edit the "ABC" text, it will update all the objects, as they refere to the same object data.